The present invention relates to fire protection and extinguishing a fire in the freight and cargo space of vehicles, particularly the baggage and freight compartment(s) of an aircraft.
It is well known that aircraft, particularly commercial aircraft, are constructed to be operated either as passenger carrying vehicles, or as freight and cargo carriers or in some kind of hybrid configuration. Passenger planes, include, of course, passenger and pilot compartment in upper decks and, in addition certain space is set aside basically for baggage but which can also be used as cargo space for air freight. This baggage compartment or bulk of the aircraft is usually in a lower deck, and is constructed, particularly for large aircraft, in that the freight and baggage is placed in containers and the containers are shifted in and out of the aircraft. Usually, this freight and baggage compartment is situated underneath the passenger compartment in regular aircraft, operated basically as passenger carrying vehicles, but in other, hybrid cases, the tail portion of the aircraft holds also baggage.
In case a fire develops somwhere in any of these cargo spaces and compartments, the principle object is to prevent the spreading of the fire, and for this fire extinguishing equipment is known and used which basically is comprised of two completely separated fire extinguishing systems, each with its own network of distributing conduits. The first one of these two fire extinguishing systems responds directly and immediately upon a signaling of smoke, and the containers for a fire extinguishing medium, being under atmospheric pressure and pressurized accordingly, will immediately and directly empty this medium fully into the particular cargo space. The rapid emptying of these containers causes a high concentration of fire extinguishing medium within the freight and cargo space so that, hopefully, the then existing fire is rapidly extinguished. The second fire extinguishing system is provided to make sure that subsequently during the remainder of the flight, the concentration of fire extinguishing material in the freight space will not drop below a particular limit. The second fire extinguishing system includes a conduit network which is provided with discharge nozzles for the fire extinguishing medium, and solid particle filters as well as extinguishing gas dryer are provided close to these nozzles. The nozzles generally are controlled to provide a relatively slow rate of flow of fire extinguishing medium, particularly at a constant rate, so as to maintain the status quo.
It is quite apparent that the second fire extinguishing equipment operates on a relatively long term basis. It was found that occasionally icing may occur, particularly in the cleaning, filtering, and metering equipment. This icing over occurs on account of the evaporation process of the emerging fire extinguishing medium which evaporation produces a very drastic drop in temperature of the joining equipment. This icing over may, in fact, render it time the second extinguishing system inoperative. Relevant prior art includes U.S. Pat. No. 4,566,542, as well as fire extinguishing equipment, e.g. for the Boeing 767 aircraft.